The oceans appear ideal for biodiversity – they have unlimited water, a large area, are well connected, have less extreme temperatures than on land, and contain more phyla and classes than land and fresh waters. Yet only 16% of all named species on Earth are marine.

This study assessed how many marine species are named and estimated to exist, paying particular regard to whether discoveries of deep-sea organisms, microbes and parasites will change the proportion of terrestrial to marine species. Then, the authors reviewed what factors have led to species diversification, and how this knowledge informs conservation priorities.

The results of this work show that species most sensitive to extinction from human activities and climate change are large megafauna and species with restricted geographic ranges. The authors state that regarding this, marine reserves are a simple, practical way to protect both groups of threatened species, as well as co-occurring species. It is highlighted that taxonomic and conservation efforts should focus on areas of high endemicity and that areas with higher habitat heterogeneity should be prioritised for conservation, as they are likely to harbour more habitats and species.

The study concludes that as a result, for conservation prioritisation, endemicity may be a better metric of biodiversity than species richness. However, it requires more taxonomic effort to distinguish species, especially rare species, and more geographically complete species’ distribution data, and one third of species may not yet even be named.

http://www.sciencedirect.com/science/article/pii/S0960982217305055

Costello MJ, Chaudhary C (2017) Marine Biodiversity, Biogeography, Deep-Sea Gradients, and Conservation. Current Biology 27:R511-R527

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